Reset root's Password (with GRUB)

If you lost your root's password, but you have GRUB boot loader installed. Here's the list of steps to reset it:

• Power up your machine and press ESC while GRUB menu starts.
• If there is a 'recovery mode' option, select it and press 'b' to boot into single user mode.
• Press 'e' (to edit) to the default menu option.
• Highlight the line with 'kernel' and press 'e' again.
• Append 'single' at the end of the line.
• Press 'b' to boot into single-user mode.

With this, you should end up getting a shell with root privilege (#).

Note, some distribution might require you to re-mount the partition (with /etc inside) with read-write:

mount -o rw,remount /dev/hda1 /

Another way is to reset password with Live CD.

• Boot the machine with a LiveCD.
• Search the partition that hold the /etc/passwd file: sudo fdisk -l
  
• Make a directory mount point: sudo mkdir /media/sda1
• Mount the partition with the mount point: sudo mount /dev/sda1 /media/sda1
• Change root to the mount point: sudo chroot /media/sda1
• Change the password: passwd root